1. Field of the Invention
The present invention relates to methods and apparatus for nuclear magnetic resonance (MR) imaging, in particular to MR methods and apparatus permitting reconstruction of MR images from signals received from an RF receiving coil which is swept over a region of interest during imaging.
2. Description of the Related Art
The clinical success of surgical tumor resection is often limited by residual tumor which remains at the completion of the procedure. This limitation is particularly common with brain tumors where access to the lesion is limited both by anatomic constraints (skull, etc.) and by the surgeon's desire to produce minimal morbidity. As a result, tumor may remain hidden from the surgeon and go undetected until post-operative imaging is performed.
Studies (see, e.g., Albert et al., 1994, Neurosurgery 34-1:45-60) have motivated the addition of intra-operative imaging modalities, including ultrasound, computed tomography (CT), and magnetic resonance (MR), in order to provide feedback to the surgeon on the status of the surgical procedure at a time when the surgeon can still react appropriately. In particular, such imaging can provide an assessment of the tissue along the border of the resection cavity that has been created by the surgical procedure and identify residual tumor.
Therefore, for this and other reasons, intra-cavity MR imaging is of particular interest. Intra-cavity RF coils for MR imaging have been proposed and developed for evaluation of the prostate (Martin et al., 1988, Inflatable surface coil for MR imaging of the prostate, Radiology 167:570-574), cervix (Baudouin at al., 1992, Magnetic resonance imaging of the uterine cervix using an intravaginal coil, Magnetic Resonance in Medicine 24:196-203), vascular wall (Hurst et al., 1992, Intravascular (catheter) NMR receiver probe: preliminary design analysis and application to canine iliofemoral imaging, Magnetic Resonance in Medicine 24:343-357; Martin et al., 1992, MR imaging of blood vessels with an intravascular coil, Journal of Magnetic Resonance Imaging 2:421-429), and esophagus. Such small internal coils offer substantial signal-to-noise (S/N) advantages over larger external coils, and thereby permit high resolution imaging of tissue in close proximity to the RF coil.
However, these intracavity coils are necessarily small, and, therefore, are necessarily limited because their region of sensitivity is thereby strictly localized. Tissue away from the RF coil is not efficiently detected with such intracavity coils. Unfortunately, an optimally large coil for intra-cavity imaging is unlikely to be available because the extent of the cavity is unique and may not be known a priori, and because access to the surgical cavity may be through an orifice of minimal diameter.
Citation of a reference herein, or throughout this specification, is not to be construed as an admission that such reference is prior art to the Applicant's invention of the invention subsequently claimed.